Preheat oven to 350°F.
Lightly grease 9-inch square baking pan.
Beat butter, brown sugar, corn syrup and vanilla in large mixer bowl at medium speed; beat until smooth.
Stir in oats. Spread in prepared pan.
Bake 25 minutes or until center is just firm. Cool slightly on wire rack.
Stir chocolate chips in small, heavy saucepan over low heat until melted and smooth. Remove from heat; stir in peanut butter until smooth. Spread over warm bars. Cool completely on wire rack before cutting.